This is a proposal that integrates methods and concepts from both psychobiology and animal learning to exploit preparations developed by the investigator that are capable of assaying the cue properties of manipulation which effect food intake to determine the information that these manipulations provide about internal state. These paradigms, which involve training rats to use the sensory consequence of food deprivation, will assess the degree to which internal cues provided by metabolic and hormonal manipulation have stimulus consequences like those produced by different levels of food deprivation. Experiments are proposed that assess the role of vagal afferents in the ability of rats to detect or utilize energy state signals arising in the gut and the role of limbic structure in the processing of energy state information. In additional experiments the PI proposes to investigate a model that he has proposed of how energy state cues actually function to control food intake. This model suggests that these signals contribute to the control of feeding by modulating how easy it is for food cues to activate when hunger signals are absent. These latter experiments represent the major portion of the proposal and depend upon the results and techniques from the experiments in Section 1. Specifically, these experiments utilize the technique of comparing behavior of animals who have received first or second order conditioning and address how manipulations that effect food intake alter performance to first or second order conditioned cues. The idea behind these experiments is that manipulations which have physiological effects on food intake should affect the ability of a cue to elicit first order conditioned responses but not second order conditioned responses. The next series of experiments addresses the issue of whether fats and carbohydrates give rise to distinct US representation and whether the substrates for the mediation of these differ. These experiments depend upon paradigm in which rats are trained to perform different responses to receive either a high fat or a high carbohydrate reinforcement. The ability of lipoprivation or glucoprivation to differentially effect the two responses will then be assessed. Subsequent experiments in this section assess the role of vagal pathways and hippocampal structures in the mediation of these responses. In the final series of experiments the direct role of the hippocampus in the mediation of feeding responses to dietary, hormonal, and metabolic challenges will be assessed. This information will provide a background for the interpretation of the lesioning experiment under the various paradigms.